Previous studies carried out at BioCurrents Research Center have demontrated that epidermal growth factor (EGF) induces large oscillations in Ca2+ efflux in immature murine cumulus oocyte complexes (COC's) that have been removed from the ovary for less than 4 hours. This response is not seen in cumulus cells detached from the egg or in denuded oocytes i.e. both components of the complex are required for the response. The aim of the present work was to use fura-2 imaging simultaneously with the Seris probe to try and elucidate some of the mechanisms of the response that we see in COC's to EGF. The first week was spent trying to establish the correct conditions for the fura-2 imaging. We were getting very inconsistent results with the loading of these cells with fura-2 and came to the conclusion that we are probably going to have to microinject the cells with fura dextran to get satisfactory results. The appropriate techniques and conditions for microinjection will n ow be esta blished at UMass before we return to BRC. During the second week work was continued using the Seris probe and looking at the effects of ryanodine and phorbol esters on the EGF response. Ryanodine either alone or added after EGF did not seem to influence Ca2+ efflux, thereby suggesting that the ryanodine receptor is probably not involved in this response. TPA (a phorbol ester that activates protein kinase C) appeared to result in elevated Ca2+ efflux both by itself and when added in addition to EGF. However, more experiments will be required to be certain of these preliminary data.